Method and a device for ozone sterilization of objects

ABSTRACT

The present invention provides a method for sterilization of objects including the steps of placing the object that should be sterilized in a closed vessel; placing the closed vessel between two high voltage electrodes; applying a high voltage between the electrodes and converting the oxygen in the air inside the closed vessel into ozone; and keeping the sterilized object inside the closed vessel as long as needed. A &#34;closed vessel&#34; includes also any form of closed container or any closed plastic bag. The closed vessel may or may not have internal electric conductors. Furthermore, the invention provides a device for ozone sterilization of objects for use in the method. The device for sterilization comprises a sterilization chamber; two parallel high voltage electrodes located inside the chamber and connected to a high voltage transformer; a closed vessel with or without internal electrodes located between the two high voltage electrodes and the object to be sterilized is placed inside the vessel; and two parallel insulators located between the two high voltage electrodes and the closed vessel.

FIELD OF THE INVENTION

The present invention relates, in general, to a method and a device forsterilization of objects. More specifically, the present inventionrelates to a method for ozone sterilization of objects such as planttissue and tools for laboratories, dentistry, veterinary etc. Thepresent invention further relates to a device for ozone sterilizationfor use in the said method. The new method, according to the presentinvention, is based on producing the ozone in a closed and portablevessel or some other package where the sterilized object can be kepttill its usage without exposing it to the external atmosphere.

BACKGROUND OF THE INVENTION

Creation and maintenance of aseptic conditions is a very importantrequirement in many scientific, medical and commercial activities.Sterilization of material, vessels and tools is an important task whenthese are to be used in biological or medical applications. Today, whenthe awareness to clean environment and clean work is higher, theimportance of clean and sterile tools is a trivial prerequisite whensurgical equipments are concerned. Laboratories for medical work or forbiological research and development need to work in sterile conditions.Any medical equipment has to be sterilized prior to its use. Dental andhairdressers tools may transfer sources of infection and shouldtherefore be sterilized every time before use. Vessels and tools fortissue culture work have to be sterilized to provide appropriate asepticenvironment required for tissue culture applications. The plant tissueitself must also be sterilized before the propagation process can bestarted. Sterilization of medical tools such as endoscopes and otheroptical tools for medical examination imposes problems related toeffective cleaning of the tools in a short period. The sterilizationmethods known today include heating, chemical disinfection, UV rays andnuclear radiation. Heating in an autoclave has been the most commonlyused procedure because of its availability and application simplicity.However, high temperatures and pressures associated with steamautoclaving place very stringent property specifications on materialsfor vessels and tools. The sterilization of some materials by heat,particularly plastics, is very limited. Sterilization of devices whichinclude optical and electronic components, which are not "autoclavable"is also problematic. Chemical sterilization techniques are commonlyavailable, but these are usually limited by toxic residues, and requiresafety precautions for human laborers. Other difficulties that may beencountered with chemicals are special regulations for application andstorage of potentially hazardous chemicals. In R&D laboratory work thechemical sterilization can also affect scientific experiments in anadverse way by its residual influence mainly on biological matter. UVand other radiation techniques generally require special instrumentsthat are not commonly available. Nuclear radiation is very effective butit can only be done in special installations. People are often reluctantto use it and it can not be used to sterilize living plant material.Therefore "cold" sterilization techniques with minimal toxicity arehighly desirable.

One potential sterilization technology is ozone sterilization. The ozoneis a gas produced on site by high voltage gas discharge or byultraviolet radiation.

Ozone sterilization has become a widely used technique for purificationof municipal water systems, particularly from bacteria. The use of ozonegenerator in swimming pool water treatment is very common. It is alsoused for sterilization of medical equipment and in the food industry.These commercial applications suggest that ozone sterilization might beviewed as a potential alternative for asepsis purposes. Advantages aresimplicity of application, flexibility in operation, minimal toxicresidue and relatively low costs. There is no need for raw materialwhich is readily available anywhere and almost no temperaturedifferences are present. It will enable sterilization of a wide range ofmaterials for equipment, tools and growing vessels.

The conventional known technique for atmospheric and surface ozonesterilization is to use a remote, high voltage discharge ozone generator(ozonator) from which ozonized air is directed to a closed vesselholding the substance to be sterilized.

Since ozone is an unstable gas, its concentration is reduced rapidlyalong its way to the point of application. Thus, in order to get therequired concentration at the application point, relatively largeozonators must be used. Larger ozonators require higher electric powerand better electric insulation measures. The higher concentration of theozone at the source calls for more precise sealings. The conventionalmethod is more suitable for large scale sterilization in relatively bigchambers where many parts are sterilized together. This conventionalmethod is not very effective in sterilizing surfaces which are notreadily exposed to the Ozone. Sterilization of encapsulated objects isnot effective at all. After sterilization, the sterilized object has tobe removed from the sterilization chamber. By the mere opening of thechamber, new infection may be caused if no special precautions are met.

Another known method is used only in very large volumes by placing theozone generator inside the large (technological) vessel. In this case,the internal surface and the whole volume are exposed to infection whilethe generator is being removed. For this reason the method did notbecome widely used for general purposes.

SUMMARY OF THE INVENTION

The present invention provides a method for sterilization of objectscomprising;

(a) placing the object that should be sterilized in a closed vessel; A"closed vessel" includes also any form of closed container or any closedplastic bag. The closed vassel may or may not have internal electricconductors;

(b) placing the closed vessel between to high voltage electrodes;

(c) applying a high voltage between the said electrodes and convertingthe oxygen in the air inside the closed vessel into ozone;

(d) keeping the sterilized object inside the closed vessel as long asneeded.

The embodiment of this invention comprises an electric conductor placedinside the closed vessel (the sterilization vessel or bag).

In some cases as narrow vessels or bags the internal conductor may beunnecessary.

However, in both cases, the ozone is produced within the closed vessel.The electric discharge is produced in the gap between the externalelectrodes and the neighboring surfaces of the internal electrode, (thepreferred position is that they will be parallel to each other).

Furthermore, the said invention provides a device for ozonesterilization of objects for use in the above mentioned methodcomprising;

a sterilization chamber; two parallel high voltage electrodes locatedinside the said chamber and connected to a high voltage transformer; aclosed vessel with or without internal electrodes located between thetwo high voltage electrodes and the object to be sterilized is placedinside the said vessel; and two parallel insulators located between thetwo high voltage electrodes and the closed vessel.

In the preferred embodiment of this device two parallel electricconductors (internal electrodes) are placed in the closed vesselparallel and adjacent to the two external high voltage electrodes, andthese two internal electrodes (conductors) are connected to each otherby a conductor.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method and a device for ozonesterilization inside a closed environment. In its preferred embodimentthe present invention provides a method and a device for ozonesterilization using an electric conductor (an internal electrode) insidethe closed sterilization vessel (hereinafter called the "closedvessel"). The electric discharge occurs in the gap between the externalelectrodes and the neighboring surfaces of the conductor inside. Theelectric discharge produces the ozone in the closed chamber from theoxygen contained in the air inside. The efficiency of the process ishigh due to the fact that the ozone is produced in the same place whereit is needed, and need not be transferred. The continuous electricdischarge also regenerates the ozone from the oxygen to which itdegenerates, being an unstable gas as explained previously. This methodwill be used to sterilize the internal surfaces of the vessel itselfwhich will be kept closed and aseptic till its usage, and the externalsurfaces of any material kept inside.

The method and system according to the invention can be used in smalland large scale. The closed vessel can be of any size and shape and canbe moved and stored including the sterilized material inside. When theclosed vessel of the material to be sterilized is small enough, theinside conductor may not be needed. For an example, sterilization ofplant material in plastic bags, can be performed in this way. Theobjective of the method and the device according to the presentinvention is as follows:

1. To improve the reliability and effectiveness of sterilization.

2. To widen the scope of usage of ozone sterilization.

3. To lower power consumption.

4. To enable production of ozone in a closed vessel which can be keptclosed for transportation to the point of usage while keeping sterileconditions inside.

5. To provide a simple relatively cheap and portable device forlaboratory and other sterilization purposes.

The new method according to the present invention is based on producingthe ozone in a closed and portable vessel or some other package wherethe sterilized object can be kept till its usage without having toexpose it to the external hostile atmosphere.

The new method according to the invention also utilizes the dielectricproperties of the package in the high voltage discharge between theelectrodes. This may be more effective in sterilizing surfaces wherehigher concentrations of ozone may be required. It enables sterilizationof the inside atmosphere of closed vessels.

The closed vessel, in this case, becomes an inherent part of thegenerator. The oxygen in the air inside the closed vessel is converteddirectly into ozone. This opens the possibility for operating smallsimple devices for use in laboratory and other commercial purposes tosterilize small tools and even plant tissue and keep it closed as longas needed, or in larger enterprises, to sterilize material enclosed incontainers on a continuously moving belt.

This method affords considerable flexibilty in establishing dosagelevels and in treating objects of various shapes and sizes. Preliminaryexperiments with plant tissue culture sterilization by ozone using themethod and apparatus of the present invention showed advantage overconventional chemical sterilization of the same.

The present invention will be further described and clarified by FIGS.1, 2 and 3. These figures do not intend to limit the scope of thepresent invention but to describe the preferred embodiments only.

FIG. 1 illustrates a side view of the device, sterilizing plant specimenin a plastic bag without any internal electrode.

FIG. 2 illustrates a side view of the device, sterilizing plant specimenin a plastic bag with an internal electrode.

FIG. 3 illustrates a side view of another preferred embodiment of thedevice having two parallel internal electrodes in the closed vesselconnected by a connector.

FIG. 1 illustrates a device according to the present inventionsterilizing plant specimen in a plastic bag. In a sterilization chamber(1) two parallel high voltage electrodes (2) and (3) are located(hereinafter also called the external electrodes). The preferred voltagebetween these external electrodes during operation is approximately 7-25KV. A plant specimen (4) is located inside a closed plastic bag (5)(hereinafter also called the closed vessel). This plastic bag is locatedbetween the two external electrodes. Two parallel insulators (6) and (7)are placed between the plastic bag (5) and the external electrodes (2)and (3). The sterilization chamber has an inlet filter (8) and an outletfilter (9) and an exhaust fan (10). The closed vessel (the plastic bag)is small and consequently the two external electrodes are adjacent toeach other, so we do not need any internal electrode. The sterilizationtime for plant specimens is about 10, 20 or 30 minutes.

FIG. 2 illustrates the same device as described in FIG. 1 but with onemain difference. An internal electrode (11) (a conductor) is placedinside the plastic bag. By using this internal electrode the electricspark is "jumping" twice, from one external electrode (3) to theinternal electrode (11) and from the internal electrode (11) to theother external one (2).

By using an internal electrode we can reduce the voltage between the twoexternal electrodes. Moreover, we can locate the plant specimen outsidethe sparking area (as is shown in the figure) and thus the plant doesnot suffer from any damage.

FIG. 3 illustrates a side view of another preferred embodiment of theinvention. This device is the same as described in FIGS. 1 and 2 exceptthe closed vessel (12).

The closed vessel has two parallel upper (13) and lower (14) internalelectrodes (conductors) connected to each other by galvonic connector(15) (conductor). During the ozonation the sparks are taking placebetween the upper external high voltage electrode and the adjacentparallel internal electrode, and between the lower internal electrodeand the external lower electrode. This ozonator as described in FIG. 3can use a closed vessel having any size and shape because the problem ofthe distance between the two external electrodes does not exist anymore.

We claim:
 1. A method for sterilization of objects comprising:placingthe object that should be sterilized in a closed vessel; placing theclosed vessel between two high voltage electrodes; applying a highvoltage between the said electrodes and converting the oxygen in the airinside the closed vessel into an ozone; and keeping the sterilizedobject inside the closed vessel as long as needed.
 2. A method forsterilization of objects according to claim 1 wherein at least oneelectric conductor is placed inside the closed vessel.
 3. A methodaccording to claim 1 wherein the objects to be sterilized are tools forlaboratories, medicine, dentistry and veterinary or plant tissues.
 4. Adevice for ozone sterilization of objects comprising: a sterilizationchamber; two parallel high voltage electrodes located inside the saidchamber connected to a high voltage transformer; a closed vessel locatedbetween the two high voltage electrodes and the object to be sterilizedis located in the said vessel; and two parallel insulators locatedbetween the two high voltage electrodes and the closed vessel.
 5. Adevice for ozone sterilization according to claim 4 wherein at least oneelectric conductor is placed in the closed vessel.
 6. A device for ozonesterilization according to claim 5 wherein two electric conductors areconnected to each other by any connector and the object to be sterilizedis located in the closed vessel.
 7. A device according to claim 4wherein the sterilization chamber has at least one filter.
 8. A deviceaccording to claim 4 wherein the closed vessel is a plastic bag.
 9. Adevice according to claim 7 wherein the object to be sterilized insidethe plastic bag is selected from the group consisting of a plantspecimen and a tissue.
 10. A method for sterilization of objectsaccording to claim 1 wherein the closed vessel has internal electricconductors.